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little yellow motors versus servo motors — Parallax Forums

little yellow motors versus servo motors

whiteoxewhiteoxe Posts: 794
edited 2014-08-11 17:30 in Robotics
Cant sleep so time for another strange question. I want to mount a camera or distance sensor with 2d of freedom. I can buy servos for $14.00 or those little yellow motors used in robot kits for $3.50 here is a link http://www.ebay.com.au/itm/371094439398?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649

what would you do ?

Comments

  • GenetixGenetix Posts: 1,754
    edited 2014-07-27 15:38
    Servos are a lot easier to program for.

    If you need precise movement then use Stepper Motors.

    How big is the camera?
  • Beau SchwabeBeau Schwabe Posts: 6,568
    edited 2014-07-27 16:16
    I have some friends that are currently working on a pan/tilt camera system.... They are using a high resolution encoder for repeatable and programmable camera positions. The problem even at high resolution is that at a distance or zooming in, even a single step form the position mechanism can translate to a large offset in the video field.

    Here is there work so far.... I was able to see some of their work about a week ago and they were fine tuning the trapezoid algorithm to minimize and eliminate overshoot error.

    http://okrobotics.com/the-pan-tilt-zoom-story/ <- And they are using a Propeller :-)
  • whiteoxewhiteoxe Posts: 794
    edited 2014-07-27 17:01
    Thx Beau, but that's a little ahead of me just now.

    @Genetix, just thinking of the cameras like those sold by Parallax. most stepper motors I found were $16 to $26 so I wonder what quality I get for 5 of them at total cost of $11, all done!

    http://www.ebay.com.au/itm/5pcs-Stepper-Motor-DC-28BYJ-48-5V-ULN2003-Driver-Test-Module-Board-for-Arduino-/311014265101?pt=AU_B_I_Electrical_Test_Equipment&hash=item4869e5110d
  • Duane DegnDuane Degn Posts: 10,588
    edited 2014-07-27 18:22
    Servos would be a lot easier to use. You should be able to get some realatively strong servos for around $10. I think erco likes these monsters. I have some but I haven't used them in a project yet.

    @Beau, Very cool pan/tilt mechanisms. IMO, some sort of DC motor with encoder is the way to go. I'm still trying to get that sort of stuff figured out.
  • kwinnkwinn Posts: 8,697
    edited 2014-07-27 19:05
    whiteoxe wrote: »
    Cant sleep so time for another strange question. I want to mount a camera or distance sensor with 2d of freedom. I can buy servos for $14.00 or those little yellow motors used in robot kits for $3.50 here is a link http://www.ebay.com.au/itm/371094439398?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649what would you do ?

    These look like DC brushed motors so you would need a dual H bridge to drive each one and an encoder or pot+adc for positioning. Probably less cost to use servos when all is said and done, but it depends on the application and precision required.
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2014-07-27 20:20
    whiteoxe,

    Based upon the experience level manifest in your other posts, I would recommend starting with an RC servo. They're relatively cheap, and they give you tremendous bang for the buck, in that they handle all of the litlle feedback and PID-control details for you. Obviously, with a geared-down little yellow brushed DC motor, a current-controlled H-bridge, an encoder, and sophiiscated programming, you could achive performance beyond that of a servo, but that's certainly not where I'd start.

    -Phil
  • Duane DegnDuane Degn Posts: 10,588
    edited 2014-07-27 20:37
    Phil Pilgrim (PhiPi) wrote: »
    Obviously, with a geared-down little yellow brushed DC motor, a current-controlled H-bridge, an encoder, and sophiiscated programming, you could achive performance beyond that of a servo, but that's certainly not where I'd start.

    +1

    I still hope to use the little motors with encoders I was experimenting with here to make some soft of pan tilt mechanism. But using DC motors with encoders as a DIY servo is far from trivial. I agree with Phil (generally a good idea) and think servos would be a much better choice in this case.
  • ercoerco Posts: 20,257
    edited 2014-07-27 20:41
    Most servos require internal mods for CR to use as motors. Stick with gearmotors and H-bridges whiteoxe. But NOT the 1:48 junk you first linked to. Completely useless junk, no torque. Ebay and Sparkfun should be horsewhipped for continuing to sell those.
  • Duane DegnDuane Degn Posts: 10,588
    edited 2014-07-27 21:06
    erco wrote: »
    Most servos require internal mods for CR to use as motors. Stick with gearmotors and H-bridges whiteoxe.

    Erco, did you see this is for a pan/tilt camera mount? In other words, ARE YOU NUTS?
  • GenetixGenetix Posts: 1,754
    edited 2014-07-27 22:36
    Whiteoxe, Phil is absolutely correct and since both objects are small and light you should have no problem using standard Parallax servos.

    I picked up 2 Parallax servos from Radio Shack when they were discounted at $1 each. I was thinking of converting them to CR for a robot. Parallax servos are actually made by Futaba.

    Duane, I don't know what Erco was on when he posted but he must have misread something.
  • whiteoxewhiteoxe Posts: 794
    edited 2014-07-27 23:18
    Do not fear, I did think of dc motors to drive with the half dozen L298 motor controllers Duane made such an ease of use , even the SN7544, I have been playing with a parallax servo that I bought sometime in antiquity and rediscovered, part of a basic stamp kit I think. It just seems easier for small movements, but Erco could have .swayed me if there were no objections !. I do have what looks like a quality stepper motor with leads to a small board , it was in a box of stuff that one of the very kind members dropped off to me ,it may be a servo actually? . I will play around with that very soon. There will be some number code on it so I can find out more about it.

    The pan and tilt mechanism is made for standard servos though. The funny thing about that unit is its the same price from both the US and Australia. $5.95 but the US postage, the least expensive of 4 options was only $3.90...must be by submarine ? The cheapest Australian postage was a bit over $7.00 or maybe nearly $8 I don't remember exactly. But recently on the forum when I nominated aus LittleBird Electronics one poster said they have a lot more listed as In Stock than they actually do So I haven't decided which to purchase but I know that every couple of bucks that I don't worry about , does end up being a lot more in the end.. I can also wait as the more familiar I get with programming motors the better prepared I will be when it comes to putting it together.

    I have bought two blue servos that looked exactly like the ones I saw in the picture of the tilt and pan mechanism., $6.00 each.

    I just got in the mail two ADC chips from RS components, reasonable price and it was only a couple of days. but you don't want to buy a propeller chip from them. They have no postage charge but the chip alone is $30. True ! They stock a lot of Parallax but all the prices from chips to boe bots are very inflated. You would have to really really need it overnight to buy!
  • ercoerco Posts: 20,257
    edited 2014-07-28 04:53
    Duane Degn wrote: »
    Erco, did you see this is for a pan/tilt camera mount? In other words, ARE YOU NUTS?

    Sorry, my bad. Asleep at the wheel.

    Keyboard.

    Carry on!
  • GenetixGenetix Posts: 1,754
    edited 2014-07-28 19:12
    I guess you had a Harold and Kumar moment, Erco.

    Stick with Servos, Whteoxe.
    In fact one person used a servo to operate a toilet because otherwise the handle needed to be held open. He pressed a button and a BS2 would hold the handle open for 10 seconds before closing it again. He even had it record the number of flushes on an LCD that sat on the top of the toilet.
  • whiteoxewhiteoxe Posts: 794
    edited 2014-08-08 16:46
    i bought without reading enough. I got two sevos in the mail yesterday thay i thought were full sized continuous rotation .

    They are tiny little things, if id paid more attention I would have noticed that they were micro servos. Will be interesting to hook them up and see how they perform. I dont expect very much .


    microservo_zps3798a66d.jpg
  • GenetixGenetix Posts: 1,754
    edited 2014-08-10 16:49
    Whiteoxe, CR means Continuous Rotation, which are used mainly for robots. Standard servos rotate from 0-degrees to 180-degrees. Since your pan/tilt mechanism doesn't spin completely around you should be using ordinary servos.
    By the way, regular servos can be modified for Continuous Rotation.
  • whiteoxewhiteoxe Posts: 794
    edited 2014-08-10 20:43
    Genetix, I have only done the basic servo experiments in WAM. I thought it would not matter if a servo had CR or Not? Might be a mistake. I think it is anyway. Im not sure I should have micro servos at all !!!
  • GenetixGenetix Posts: 1,754
    edited 2014-08-10 23:43
    Whiteoxe, I doubt if your pan/tilt mechanism will work with a micro servo. Try it. More importantly though is you need the position control that only a standard type servo gives you.

    CR servos go round and round and all you can control is the speed and direction.

    I think it was Erco who found servos at Hobby King for $6.
  • whiteoxewhiteoxe Posts: 794
    edited 2014-08-11 17:30
    HobbyKik is really stocking a lot more item than a few years ago. They sell HobbyKing Servos and other brands. Also stuff like sensors. Robitics section to.

    Im srtill waiting on the pan tilt mechanism to see what sevos i have will work with it.
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